A problem existing in the mechanical engineering is associated with production of high-precision long-size tubes from difficult-to-form metals and alloys used in particular in manufacture of jackets for runover rolls of textile finishing machines and impression rollers of rotary printing machines. Very stringent requirements are imposed upon the accuracy of manufacture of such tubes, as an increase in the rotational speed of the rolls or rollers intended to step up the output of the machines may cause intensive oscillations and rupture of the moving material (textile fabric, paper tape). For example, in the jackets for runover rolls of textile finishing machines with the length of the roll amounting to 2200 mm, the runout must not exceed 0.4 mm.
Known in the prior art are apparatuses or production of such tubes, wherein a tube is sized in a die under the pressure of flulid.
There is known an apparatus for sizing of tubes intended for production of rollers for printing machines (cf. USSR Inventor's Certificate No.606,538 published in the journal "Discoveries, Inventions, Industrial Designs and Trademarks", 1978, No.17), comprising a die with a sizing channel in which a tube is installed. Inserated in the tube interior with the purpose of reducing the unbalance of these rollers is at least one additional tube which is shorter in length and whose outside diameter is equal to the inside diameter of the tube being sized. An elastic bag is introduced in the space of the tubes and the ends of the tube blank are hermetically sealed with stoppers. Deformation of the tubes is accomplished by pressure of the forwking medium delivered from a static pressure source into the elastic bag along a pipeline passing through one of the die end stoppers.
Due to a static character of the tube blank loading, such an apparatus cannot ensure a high level of accuracy in sizing of tubes.
Besides the apparatus is inconvenient in servicing.
The preparatory operations associated with installation of additional tubes in the main tube and also with introduction of the elastic bag in the interior of these tubes are substantially labour-and time-consuming.
Also known in the prior art is an apparatus for sizing of tubes under the pressure of fluid (cf. USSR Inventor's Certificate No.377,181 published in the journal "Discoveries, Inventions, Industrial Designs and Trademarks", 1973, No.18) in which a tube is sized portionwise. The apparatus comprises a split die mounted on a bed and provided with a horizontally arranged sizing channel corresponding to the shape of a tube, which accommodates a mandrel for setting the tube coaxially with the sizing channel, a means for delivery of fluid in the hermetically sealed clearance between the mandrel and the tube, and a means for building up the pressure of fluid in the clearance between the mandrel and the tube. The mandrel is provided with passages for delivery of the fluid into the clearance between the mandrel and the tube. At the ends the mandrel has circular grooves which are connected with the passages for delivery of the fluid and accommodate elastic packings which hermetically seal the clearance between the mandrel and the tube. The die is installed for a reciprocating movement along the guideways provided on the bed and arranged parallel to the mandrel. The halves of the die are opened and closed with the aid of hydraulic cylinders which also take up the pressure transmitted to the die in the process of sizing. The tube is moved for a successive sizing by means of a carriage provided with a centering device for one end of the tube being sized.
By means of the carriage the tube is pushed in the die set in one extreme position, then the die is closed and the tube complete with the carriage and the die is moved further along the guideways to the other extreme position of the die, thereby slipping the tube portion encompassed by the die over the mandrel for sizing. Then the fluid is delivered into the clearance between the mandrel and the tube, and the latter is plastically deformed when the predetermined pressure of fluid is reached. Thereafter, the die is opened, moved through one step backward in the direction of a non-sized portion of the tube, closed again and slipped complete with the tube over the mandrel for sizing the next portion of the tube. The return movement of the die is necessary to preliminarily aliminate ovality of the tube portion before its sizing.
In the process of static sizing under the pressure of fluid the tube expands and from the beginning of deformation till the moment the tube comes in contact with the die wall, the tube blank is subjected to a free expansion characterized by an unfavorable pattern of the state of stress, with the result that the plastic flow of metal is not uniform due to the presence of weakened areas (defects, thinned wall) in the tube material. This condition reduces the quality of tubes received after sizing.
When tubes are manufactured from strain hardening materials (for example, stainless steels) the succesive portionwise sizing leads to a premature hardening of the material at the boundary of the sized and non-sized portions of the tube. This increases the nonuniformity of stresses set up at a successive tube portion in the process of its sizing, and thereby changes the spring back of the material at the boundaries of the tube portions. This condition also impairs the quality of tubes as the production of precision tubes with the sizing performed under the static pressure of fluid is possible only when the value of the material spring back after removal of the load is taken into consideration.
The successive portionwise sizing cannot provide for an accurate contour of the tube shell along the generator (i.e. it cannot correct the tube curvature) as the sizing portion of the apparatus, the split die, is moved along the guideways relative to the fixed mandrel. As a result, an error caused by nonparallelism in movement of the die and by different settings of the die on the guideways will be introduced in the total error.
The apparatus described herein before has a low output resulting from the multiple loading required in the portionwise sizing. The total time required for sizing a tube throughout its full length is practically as many times greater than a single cycle of sizing a separate portion of the tube as many times the tube length is greater than the length of the die sizing portion, since the sizing of each new portion of the tube necessitates repetition of all the steps needed for accomplishment of the given operation.
In addition, the ends of tubes remain non-sized due to the fact that the clearance between the mandrel and the tube is sealed on the tube inside diameter with the aid of packings installed in the circular grooves provided on the external surface of the mandrel. These non-sized ends of tubes should be cut off (which increases consumption of the material) or any other method should be used for correcting the remaining defects.